Sudden blade pitch / pop up - RC Groups
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Apr 20, 2007, 02:28 PM
KJ4IKY Gravity Wins
blade thrasher's Avatar

Sudden blade pitch / pop up

I have made the modification to the stepped washers as shown in the CAD illustration but am still having some sort of sudden pitch change. At about half throttle my CP2 will lift off and I can hold a steady hover then all the sudden it will pop up quick enough to send it from the middle of the garage into the overhead door. The changes are so erratic and sudden it is almost impossible to control .

When I hold it and throttle up it appears fine and no pitch change, good alignment.


added Superskids
rebuilt entire rotorhead assmbly, made sticky collective fix,
new blades
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Apr 20, 2007, 10:50 PM
Psurvival = 1/ThArrival
osterizer's Avatar
There are a lot of things that can make this happen, usually involving either a jumpy servo, a sticking ball joint/swash/hub carrier/grip hinge/&c, or (occasionally) a ball link popping off onto the neck of the ball.

That being said, if you replaced a significant number of parts, I'd look at the spindle to make sure all the bearings and washers are in the right place and turned the right way, make sure the swashplate and hub are free, and that the ball links are also-- you almost always have to size the rings on new parts.
Apr 21, 2007, 12:14 AM
BeeZaur 480
BowerR64's Avatar
Before i got my CP thats one of the first things i read was the CP was prone to sticky or tight ball links causing it to go from a low to full pitch without notice. Does it do it everytime you fly? what if you just hold the heli and watch what it does? You should see the servo stick or move if the servo tape is loose.

You know how a car is hard to turn the wheel when the car is not moving, but once its moving the wheel becomes easy to move. Maybe its similar to this?
Apr 21, 2007, 12:22 AM
Team Mulikow
Gino CP's Avatar
You can check for a sticky head by removing each long pitch link from the swashplate. Move the links and see if you have a free see saw action. Any binding will show up there.

If that is good, pull each blade grip apart slightly and move blades positive and negative. Note any binding. If there is binding, it has much to do with washers and bearings.

If those check out ok, inspect your pitch.Set pitch by hanging heli from the paddle control frame. This accounts for slop and will give you true hovering pitch. Set pitch to zero. Adjust tracking by adding positive pitch to low blade. (Bad tracking can cause jumpiness too). Tracking less than half an inch is pretty normal for the CP2 hehe.

Test hover. If it is jumpy, add half a turn to each long pitch link to increase pitch. Test again. Do so until jumpiness is gone.

Next time you fly listen to the head speed. If it is unusually high and there is no lift, it is a time bomb. Once that binding lets go, up she goes.
Apr 21, 2007, 01:14 AM
BeeZaur 480
BowerR64's Avatar
When i got my CP there were a few parts in the box, a few of the parts were some bearings, and some blade grips. I then looked closly at the blades and the grips and found some slop in them pulling them outwards. When inspecting the old grips i noticed a bearing inside one of them so i had a feeling it wasnt put back together right.

When i painted the blades to look like knifes i then decided to rebuild the head where the blade grips connect.

I was to say the least shocked how much junk is in there. I dont understand all these parts. I mean there are 2 bearings stacked, on each side. whats the pourpose of this? all these washers, and orings and WTH? i can see how this can cause problems or binding. You NEED the manual just to get all these parts stacked correctly just to know that you have it together right.

IMO there really is to much to this section of the head. It seems like just alot of crap to make up for a part that is designed for another heli.

I mean look at all the parts

I know this is a critical part of the head and how it functions, but when you add this many parts its just that much more to fail, lockup, get dirty, be rebuilt wrong or what ever. Im sure if its not pefect, the pitch will probobly bind.
Last edited by BowerR64; Apr 21, 2007 at 01:21 AM.
Apr 21, 2007, 01:54 PM
Psurvival = 1/ThArrival
osterizer's Avatar
Well, BowerR64, the thing is, it's complicated because it needs to be. The head you pictured is a Bell-Hiller setup, which performs mechanically a mixing between control input and disc stabilization that we are only now seeing electronics coming out to accomplish in models-- either way it has to be done somewhere in a CP heli.

The reason for the dual bearings is to stabilize the grips on the feathering shaft (only one would not be sufficient). The stepped washers put the load on the inner race instead of both (which would lock the blade grips). The bearings are there in the first place to enable the grips to turn smoothly even when loaded up at flight speed. The o-rings are there to enable damped flapping motion (up and down), which is required to even the lift out in the rotor system.

Basically, there's nothing there that doesn't have a purpose. The manufacturers of these things try to keep costs down and performance up, so where they can simplify, they do. There are a number of sites (and threads on this site) to explain in a lot more detail some of the things I've touched on above; if you take a look around and read up on how they work, you'll find it's pretty interesting stuff. Personally I appreciate the ingenious way the bits fit together and work.

And yes, , if you get anything wrong it won't work well, and it can be very annoying figuring out what it is!
Apr 21, 2007, 04:26 PM
Registered User
i had that problem on a new ranger 3d. the only thing i found wrong was a tiny amount of play in the main shaft. if i gently twisted the blades back and forth i could see it. I tightened that and the problem went a way.
Apr 24, 2007, 03:33 PM
KJ4IKY Gravity Wins
blade thrasher's Avatar
I havent had a chance to test out the posted fixes. While I was trying to figure out what was causing the sudden pop in pitch it popped and went quite high, spun and came straight down. Luckily there was a small patch of concrete in the grassy field to break its fall. somehow while it was falling I decided I would try to catch it. When I reached out the strap flipped the throttle to full just before it hit the concrete.

1 main shaft that looks like a boomarang
1 blade control arm
1 cyclic control arm
1 servo
landing gear strut (super skids)
tail skid strut (super skids)
tail axis
2 blades

Now I have more important problems to figure out. What would cause all the servos to constantly glitch and sudden motor spinning? Oh, and the battery had also been tossed out in the crash and the 4-in-1 was hanging by the servo cables.

Any suggestions? Hopefully I dont have to buy a new 4-in-1.
Apr 24, 2007, 05:50 PM
BeeZaur 480
BowerR64's Avatar
When i got into this i first got a picoo and had a blast but i wanted more so i came to the forums. As i was reading around i read a post or some one told me to get a flight sim one thing lead to another and i wound up buying my first good heli, blade CP for the controler to use on the PC

I figured i could use the controler to learn with, then when i was ready the blade CP would be there waiting. After some struggeling with programs i figured out all the stuff i needed and i was flying FMS with my CP controler. While i was doing that i noticed that when ever i got into a menuver where i had to give full bottom right stick (rear pitch) the heli would go nuts and crash. Even when i went to the calibratioin and i gave full down pitch all the bars would do somthing weird. I didnt know if it was the controler, or the programs i was using to get the CP controler to work on the PC or what. So i just dealt with it. I then bought a CX and i tried that controler and it didnt do it. Then i got a pro, its controler was REALLY good and smooth. So now i have it narrowed down to the controler.

I took the controler apart and i sprayed motor/electronic cleaner into all the pots. No more freaky weird glitch from that controler, now its just as smooth as the pro. If i had tried to fly my CP with this controler i may have crashed it.

If your controler is doing weird stuff, test it with the sim, see if the sim helis act the same way. Its worth a shot to test it IMO

sorry that was so long.
May 24, 2007, 04:50 PM
KJ4IKY Gravity Wins
blade thrasher's Avatar
You might have been right. I bought a DX7, piccoboard plus with heding hold and AR61 Rx with Spektrum servos. now it doesnt have that problem any more.

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